The closure of the tunnel was part of a bigger project to revamp Queen Street to enable longer, faster trains to run from the station.

Trains to Edinburgh, Stirling and Aberdeen were diverted to low-level platforms or Glasgow Central while the wrok was being carried out.

Since the high level station closed on March 20, over 2,000 engineers have worked over half-a-million hours to complete the £60 million project by last Friday (August 5) – nearly three days ahead of schedule – and train services were reintroduced over the weekend.

Engineers have been working around-the-clock to renew 1,800m of concrete slab track and install more than 4,000m of new rails through the structure.

The floor of the tunnel has been lowered and electric pylons have been installed.

Transport Minister Humza Yousaf said: “I am pleased to see the work on the Queen Street tunnel completed ahead of schedule and on-budget.

“This has been an unprecedented project, both in engineering terms and in the scale of the operation required to keep people moving and services diverted via the underground platforms during the works.

“This is a key milestone in our programme of investment for Scotland’s railways and literally paves the way for the introduction of a new generation of electric trains.”

Phil Verster, managing director of the ScotRail Alliance, said: “The successful, early delivery of this project will allow us to introduce faster, longer and greener trains on the main Edinburgh-Glasgow line - delivering thousands of extra seats, shorter journey times and improved accessibility for customers.”

Work to redevelop Glasgow Queen Street station is due to begin later this year with completion expected in 2019.